1. Field of the Invention
The present invention relates to a speed reducing device for electrical equipment used in a vehicle, such as an automobile, a bus or a truck.
2. Description of the Related Art
Usually, a speed reducing device of this kind employs a rubber damper which is provided as a power transmitter from a worm wheel engaged with a worm gear on a motor shaft to an output shaft of the device so as to absorb shocks. Such a speed reducing device is disclosed in Japanese Patent Laid-Open No. 60-73982 and Japanese Utility Model Laid-Open No. 62-82457. The basic construction of such a device is shown in FIG. 7. A casing 10 has a cylindrical hub portion 10a. An output shaft 11 is placed through the hub portion 10a and is rotatably supported by a bearing 12 provided on the inner periphery of the hub portion 10a. A worm wheel 14, engaged with a worm gear 13, is rotatably supported on the outer periphery of the hub portion 10. A plate 15 is coupled to the worm wheel 14, and another plate 16 is rigidly connected to the output shaft 11. The plate 15 and the plate 16 are connected by means of a rubber damper 17, which is elastically twisted to absorb shocks in power transmission from the worm wheel 14 to the output shaft 11.
However, when the rubber damper 17 is twisted, the axial ends thereof, i.e., the portions attached to the plates, receive substantial stress. If adhesion between the rubber damper and the plates is not sufficiently strong, the rubber damper may separate from the plates. In addition, the plates must be formed of a material having substantial strength, such as a metallic material. The output shaft 11 requires a bearing provided solely for the output shaft, in order to mount it on the casing. These circumstances prevent reduction of the weight of the device.